The present invention relates to an evoked potential monitoring system. More particularly, it relates to a stimulator handpiece useful as part of an evoked potential monitoring system and to remotely dictate a changeable stimulation energy level delivered by a stimulus probe otherwise carried by the handpiece.
Electrophysiological monitoring assists a surgeon in locating nerves within an obscured surgical field, as well as preserving and assessing nerve function in real-time during surgery. To this end, evoked potential monitoring, such as electromyogram (EMG) monitoring, is commonly employed. In general terms, sensing or recording electrodes are coupled to appropriate tissue (e.g., cranial muscles innervated or controlled by the nerve of interest, peripheral nerve, spinal cord, brainstem, etc.). Electrical stimulation is then applied near the area where the subject nerve may be located. If the stimulation probe contacts or is reasonably near the nerve, the applied stimulation signal is transmitted through the nerve to excite the innervated tissue. Excitement of the related tissue generates an electrical impulse that is sensed by the recording electrodes (or other sensing device). The recording electrode(s) signal the sensed electrical impulse information to the surgeon for interpretation in the context of evoked potential. By way of reference, evoked potential is a relatively generic phrase that generally encompasses any system in which a stimulus is applied and a patient's response to the stimulation is recorded. EMG is but one evoked potential monitoring technique, and can provide additional information of interest to a surgeon. For example, EMG provides the reporting on individual nerve roots, whereas evoked potential monitoring, such as motor evoked potential monitoring, provides feedback on spinal cord function.
Evoked potential monitoring is useful for a multitude of different surgical procedures or evaluations that involve or relate to nerve tissue, muscle tissue, or recording of neurogenic potential. For example, various head and neck surgical procedures require locating and identifying cranial and peripheral motor nerves. Spinal surgical procedures often utilize motor evoked potential stimulation (e.g., degenerative treatments, fusion cages, etc.). While substantial efforts have been made to identify useful implementation of evoked potential monitoring, and the analysis of information generated during these monitoring procedures, certain aspects of evoked potential monitoring have remained essentially constant over time. In particular, while stimulator probes have been modified in terms of size and shape to best satisfy anatomical constraints presented by various procedures, operational capabilities of the stimulator handpiece itself continue to be fairly basic. Namely, the stimulator handpiece maintains the stimulator probe and is electrically connected to a separate control source. The surgeon manipulates the handpiece to position the probe, but can only control stimulation levels at the separate control source.
By way of example, surgery to the spine often necessitates a stabilization of the spinal column through the use of reinforcing rods and plates. The rods and plates are affixed by screws (i.e., “pedicle screws”) fastened to pedicles, or bony surfaces, of selected vertebrae. To facilitate the attachment of the rods and plates, holes for the pedicle screws are bored into the selected vertebrae. The location of the pedicle holes is carefully determined to avoid impinging adjacent nerve roots. With this in mind, a surgeon creating pedicle holes has a desire to monitor the location of each pedicle hole and to ensure the integrity of the adjacent nerve root. Electrical stimulation is commonly used to evaluate the placement of a pedicle hole.
Current techniques for evaluating pedicle holes via electrical stimulation employ a handpiece maintaining a stimulation probe that is electrically coupled to a separate control source. The probe is inserted into a previously formed pedicle hole and stimulation at a first level applied thereto via operation of the separate control source. Assuming that no physical movement of the patient occurs (i.e., no nerve response), the stimulation level is incrementally increased, again by operating the separate power source until a desired, maximum stimulus level is applied with no visible patient response. Alternatively, Neubardt, U.S. Pat. No. 5,474,558, described a pedicle hole stimulator handpiece maintaining four switches that correlate to on/off, and three discrete stimulation levels. Use of the Neubartd device relies on physical movement of the patient to indicate pedicle hole mis-placement, and thus does not represent a true evoked potential monitoring system. Further, the discrete levels of stimulation control afforded by the handpiece inherently limits the stimulation level, and delivery thereof, desired by the surgeon.
The stimulator handpieces associated with other evoked potential monitoring system are similarly limited. Therefore, a need exists for an improved stimulator handpiece useful as part of an evoked potential monitoring system.